Project Summary/Abstract Dysregulated renal repair/regeneration leads to the development of chronic kidney disease (CKD) after acute kidney injury (AKI). However, there are no effective treatments to improve the renal repair/regeneration process, and the dearth of therapeutic options leaves affected patients at high risk of CKD progression and CKD- associated cardiovascular events and mortality. This unmet medical need underscores the importance of identifying new therapeutic strategies by elucidating the molecular underpinnings of impaired renal repair. Highly regenerative SRY-box 9 (SOX9)-expressing tubular epithelial cells (hereafter, Sox9-progenitors) were recently identified as a critical cell population for healthy renal repair. We found that Sox9-progenitors become dysfunctional, losing their regenerative function after severe but not mild AKI. Our extensive preliminary data further indicate that excess oxidative stress contributes to the dysfunction of Sox9-progenitors through ferroptosis, a newly identified form of oxidative-stress-induced, non-apoptotic regulated cell death that is observed in human AKI. Our preliminary data also underscore the therapeutic potential of harnessing anti- ferroptotic defense pathways to enhance renal epithelial repair and avert progression to CKD. However, molecular mechanisms underlying oxidative stress-induced Sox9-progenitor dysfunction remain unknown, and the contribution of ferroptosis to the AKI-to-CKD transition requires elucidation. To advance this promising and clinically relevant line of investigation, we will test our central hypotheses that: (1) In the setting of severe tubular oxidative stress in AKI, Sox9-progenitors become dysfunctional, impeding renal repair/regeneration, and (2) excess lipid-peroxidation in Sox9-progenitors induces ferroptosis, precluding healthy healing of damaged renal tubules, thus driving progression to CKD. To test these hypotheses, we will integrate unbiased single-cell transcriptomics and mouse genetics in two Specific Aims. In Aim 1, we will determine the mechanisms of Sox9- progenitor dysfunction at single-cell resolution by comparative analyses of kidneys that underwent severe versus mild ischemic renal injuries. In Aim 2, we will investigate ferroptosis in Sox9-progenitors as a key driving mechanism of the AKI-to-CKD transition by genetically deleting the anti-ferroptotic defense enzyme, glutathione peroxidase 4, from the Sox9-progenitors. We will subject our gene-modified mouse lines to ischemic, toxic, and obstructive renal injuries to define the contribution of ferroptosis of Sox9-progenitors across the spectrum of different AKI etiologies. Completion of these aims will allow us to identify molecular mechanisms of maladaptive renal repair and elucidate the fundamental pathogenic roles of ferroptosis in renal tubular epithelial progenitors. Our results will lay the scientific foundation for activating anti-oxidative and anti-ferroptotic pathways to enhance renal repair/regeneration as a novel therapy to disrupt the AKI-to-CKD transition.